1. Technical Field
The present disclosure relates to an antenna device, and more particularly to an antenna device including two monopole antennas.
2. Description of Related Art
In recent years, different types of wireless communication signals applied in technically advanced consumer electronic products have been prosperously developed, such as the signals of AM/FM, global system for mobile communications (GSM), global positioning system (GPS), satellite digital audio radio service (SDARS), digital video broadcasting (DVB), etc. In addition, the wireless communication devices applied to automotive electronics are also benefited by the evolutions of consumer electronic products and wireless communication signals. Therefore, it has become a development trend of the automotive electronics for manufacturers to integrate antenna devices of various wireless communication systems recently.
Since having a simple design and features of small volume and high gain relative to a dipole antenna a typical monopole antenna can be easily applied to vehicle-use communication systems. However, with regard to the monopole antenna for receiving a low-band frequency (e.g., 700 MHz), the length of the monopole antenna is too long in consideration of the mechanism limit resulted from wind pressure generated by a moving car. On the other hand, a vehicle-use antenna can be disposed on a car roof, and protected by a fin-shaped shell from being damaged by sun, rain, or wind. However, within a limited space, a plurality of antennas are often needed to be placed for receiving different types of wireless communication signals. Since long term evolution (LTE) techniques use many frequency bands and most of them are broadband designs, such that they are very challenging to the two monopole antennas with multiple input multiple output (MIMO). For example, because being significantly high, the low frequency receiving portion of the LTE antenna is limited by the space of the fin-shaped shell.
Moreover, the two monopole antennas with the typical MIMO need to have a sufficient distance therebetween to improve isolation. Therefore, when being disposed in the fin-shaped shell, the two monopole antennas may easily lose the original features of MIMO antenna due to significantly high mutual coupling effect.